Rear main bearing oil seal

[Ruairidh Dunford]

What is the ref: number on the seal you have?

[Parazine]

I would also like to know the answer to this question. I fitted a Viton seal to the Chummy engine when it was rebuilt, together with a speedy sleeve, The engine is reasonably oil tight under normal circumstances but prolonged high revs and hard pulling will cause a quite bad leak.

Crankcase pressure???

[Brice]

The combination that appears to be working for me at the moment (no drips)...is a new rear main cover plate, Viton seal 48x72x10 (as mentioned in the thread), 1.872-1.878 repair sleeve (as mentioned in the thread), extra breather holes in the aluminum valve chest cover along with a breather fitted to the oil filler pipe, and Comma 20/50 classic oil (maybe a contributing factor, as I was using halfords classic 20/50 oil previously).

[Ruairidh Dunford]

Brice - have you converted 48mm to inches?

Several things to consider here, the lip seal replaces a previously open area, 20/50 behaves very differently to straight 30, does Viton behave properly for this specific environment and can metric seals be used successfully on imperial bosses?

I don't have answers for these, but knowing the answers may reveal the issue/s and potential solution.

I am minded of advice that my father gave me many years ago, "Think carefully when you change something on an Austin Seven, it may have (as yet) unknown consequences down the line..."

[Steve Jones]

Looking at my notes from previous engine builds I've used metric 48x72x10 lipseals when fitting a billet rear main cover and imperial 1.87x2.81x0.31 when using a cast cover. Speedi-Sleeves fitted in both cases. Both seals still doing what oil seals are supposed to do.

Steve

[Brice]

Hi Ruairidh,

I had three different lip seals to hand, with which to choose from, two from cherished suppliers (one nitrile metric, the other is a viton possibly imperial) and one from another company, in this application I chose the viton metric. 

I have another car that leaks (straight 30 oil), so will be removing the engine and trying to replicate the process using one of the remaining seals.

Very true with regards the oil, my choice is only dependent on that it is a known crankcase to me (clean) so feel ok to use 20/50 in this instance, comma as switched from halfords own brand.


Kind regards,
B

[leaf200]

The seals have a very tight tolerance and if fitting directly to the fly wheel you must use an imperial seal. If you use a metric seal you need to fit a speedy sleeve to change the size of the boss. I found this out having fitting a metric seal and it leaked badly as was not within tolerance but felt like it fitted ok.

[Dave Mann]

Eureka, thanks Ruairidh, the leaking seal is a Grufero TC 48 x 72 x 10 it was one of five supplied 7 years ago 4 loose and one in a replacement seal plate which was a NAK 1.875 x 2.875 x 0.375. It was the NAK seal I referred to when repairing the flywheel boss 0.020” undersize and eccentric which a Speedi sleeve couldn't do. So the NAK seal should do the job. The Grufero 48 mm seal seal is 1.889” and to fit that I'll need a Speedi sleeve. The moral is to check everything. Which confirms Leaf200's point.

[Dave Mann]

The NAK 1.875 x 2.875 x 0.375 cured the problem with no leak over an hours run. Hardly surprising the metric seal leaked with a shaft tolerance of 48.00 to 47.84 when 1.875" is 47.625.

[Ruairidh Dunford]

Good news, Dave.